The present invention relates to a composition and its use in forming corrosion inhibiting and adhesion promoting coatings on metal surfaces. More particularly, the present invention relates to water-soluble or water-dispersible polyphenolamine compositions and their use as metal treatment compounds.
One means of minimizing the impact of corrosion on metal surfaces has been to coat the surface with paint. The paint acts as a barrier between the metal surface and the environment and thus helps prevent or at least minimize corrosion of the metal surface. However, one problem associated with this solution is that the paint does not always adhere properly to the metal surface. The result may be peeling, cracking, blistering, or flaking of the paint, thus rendering the substrate metal surface again subject to corrosion.
The need for applying protective coatings to metal surfaces for improved corrosion resistance and paint adhesion is well known in the metal finishing and other metal arts. One attempt to alleviate the problem for adhesion of paint to metal surfaces has been to subject the metal surface to a treatment which is known as phosphating, i.e., a process whereby a metal surface is treated with chemicals which form a metal phosphate conversion coating on the metal surface. Such a treatment typically assists in rendering the metal less subject to corrosive attack and, at the same time, in rendering the surface more suitable for application of a protective coating such as paint. The resulting bond between the metal surface and the paint is thus greatly improved. However, phosphate baths require that precise formulations be maintained and that the process procedures and conditions of operation be controlled within narrow limits. The phosphating process also requires that the metal surface be given two rinses subsequent to the phosphating bath, the first being a water rinse and the second being a passivating solution rinse which further enhances the corrosion resistance and adhesion characteristics of the coating. Traditionally, conversion coated metal surfaces have been given a second rinse with a solution containing a hexavalent chromium compound.
Lindert, U.S. Pat. No. 4,433,015 teaches that because of the toxic nature of hexavalent chromium compounds, expensive treatment equipment must be used to remove chromates from effluent water to prevent pollution of rivers, streams and drinking water sources. Hence, in recent years there have been research and development efforts directed to discovering effective alternatives to the use of such post-treatment solutions. Lindert teaches that an alternative to the hexavalent chromium compound is a polymer having phenol groups attached along an ethylenic polymer backbone. The phenol groups may have an amine substituent, which may further comprise hydroxy-alkyl groups. The polymer, made water-soluble through neutralization of the amine moiety with organic acid, may be employed in an acidic or basic solution. It is also taught by Lindert that the solution, in addition to being used as a post-phosphate rinse, may be used to treat previously untreated metal surfaces including aluminum and zinc.
Frank et al., U.S. Pat. No. 4,466,840 teaches that there is a need for a simple means to achieve results similar to that obtained with a phosphatizing process without the complexity of such a treatment. As an alternative to such a phosphatizing treatment, Frank et al., proposes employing hydroxybenzylamines, preferably in an aqueous solution, to produce coatings on metal surfaces, which coatings act as corrosion inhibitors and adhesion promoters. The amine moiety of the hydroxybenzylamines comprise secondary amines having alkyl substituents.
Siegl et al., U.S. Pat. Nos. 4,790,878 and 4,830,680 teaches the use of unique diphenolamines in an aqueous acidic solution useful to deposit an adhesion promoting and corrosion inhibiting coating on metal surfaces.
Siegl et al., U.S. Pat. Nos. 4,770,727 and 4,840,667 further teach the use of unique diphenolamine oligomeric metal-chelating compounds useful to deposit an adhesion promoting and corrosion inhibiting coating on metal surfaces. These compositions, in which the mole ratio of amine reagent to phenol reagent is 1:2, are compositionally different than the compositions of the present invention.
The present invention is directed to new polyphenolamine compounds and their use as corrosion inhibiting and adhesion promoting treatments for metal surfaces. The polyphenolamine compounds of the present invention are prepared via any suitable route, preferably via the Mannich reaction of a phenol, an aldehyde and a mixture of amines. The polyphenolamine compounds of the present invention are water-soluble or water dispersible compounds. The most preferred compound is prepared via the Mannich reaction of p-cresol, formaldehyde and a mixture of ethanolamine and polyetheramine. The polyphenolamine compounds of the present invention have been found to be particularly effective at depositing an adhesion promoting and corrosion inhibiting coating on a metal surface.
The present invention is directed to new polyphenolamine compounds and their use in treating metal surfaces to enhance the corrosion resistance and adhesion properties thereof. The compound comprises a water-soluble or water-dispersible compound selected from compounds having the general chemical formula:
Axe2x80x94Lxe2x80x94POHxe2x80x94[xe2x80x94Lxe2x80x94Axe2x80x94Lxe2x80x94POHxe2x80x94]xxe2x80x94Lxe2x80x94Axe2x80x83xe2x80x83Formula 1
wherein segments xe2x80x9cAxe2x80x9d (amine), xe2x80x9cLxe2x80x9d (aldehyde), and xe2x80x9cPOHxe2x80x9d (phenolic compound) are formed by reaction of the amine, aldehyde, and phenolic compound, for a time and under conditions sufficient to form a polyphenolamine of Formula 1. This synthesis technique is known to those skilled in the art as being exemplary of the Mannich reaction.
The segment xe2x80x9cAxe2x80x9d in Formula 1 is the unit formed after reaction of one or more amines. Exemplary amines encompassed by xe2x80x9cAxe2x80x9d include, but are not limited to, substituted or non-substituted C1-C18 alkyl or aryl primary and secondary amines, such as ethanolamine, benzylamine, laurylamine, 2-(methylamino)ethanol, allylamine, and (aminomethyl)phosphonic acid; aminoacids, such as glycine, alanine, glucosamine, and iminodiacetic acid; polyetheramines, such as the Jeffamine(copyright) series of products commercially available from Huntsman Corporation; mixtures of any of the foregoing and the like; with the proviso that xe2x80x9cAxe2x80x9d is not encompassed entirely of secondary amines.
The segment xe2x80x9cLxe2x80x9d in Formula 1 is the unit formed after reaction of one or more aldehydes. Exemplary aldehydes encompassed by xe2x80x9cLxe2x80x9d include, but are not limited to, formaldehyde, benzaldehyde, mixtures of any of the foregoing and the like. The formaldehyde utilized in the reaction may be either an aqueous solution optionally stabilized with methanol, an alcoholic solution, or paraformaldehyde.
The segment xe2x80x9cPOHxe2x80x9d in Formula 1 is the unit formed after reaction of one or more phenolic compounds. Exemplary phenolics encompassed by xe2x80x9cPOHxe2x80x9d include, but are not limited to, phenolic compounds that possess at least two reactive sites, such as cresol, nonylphenol, catechol, resorcinol, mixtures of any of the foregoing and the like. As would be understood by one skilled in the art in view of the present disclosure, it is intended that such phenolic compounds contain at least two sites that would be susceptible to the Mannich reaction.
The molar ratio of A:L:POH may fall within the range of 1:1:1 to 1.5:2:1. In this regard, the molar percentage of xe2x80x9cAxe2x80x9d, xe2x80x9cLxe2x80x9d, and xe2x80x9cPOHxe2x80x9d must add up to 100%.
In a preferred embodiment of the invention the polyphenolamine compound for treating metal surfaces to enhance the corrosion resistance and adhesion properties thereof is represented by the following formula: 
wherein R1 is a substituted or unsubstituted C1-C18 alkyl or aryl, CO2M, SO3M, or mixtures thereof; M is hydrogen, a water-soluble cation, or mixtures thereof; x is 1-100; R2 is hydrogen, a substituted or unsubstituted alkyl, aryl, hydroxyalkyl, xe2x80x94[xe2x80x94CH(R3)xe2x80x94CH2xe2x80x94Oxe2x80x94]nxe2x80x94R3, or mixtures thereof; R3 is hydrogen or a C1-C18 alkyl radical; and n is 1-100.
In a particularly preferred embodiment of the invention the polyphenolamine compound is prepared by reacting a mixture of ethanolamine and Jeffamine(copyright) XTJ-506 with formaldehyde and p-cresol, then isolating the composition as an aqueous salt solution, to yield a composition represented by the following formula: 
wherein x is 1 to 25, R1 is xe2x80x94CH3, R2 is a mixture of xe2x80x94CH2xe2x80x94CH2xe2x80x94OH and xe2x80x94[xe2x80x94CH(R3)xe2x80x94CH2xe2x80x94Oxe2x80x94]nxe2x80x94CH3, n is approximately 22, R3 is approximately a 19:3 molar ratio of hydrogen to C1 alkyl, and R4 is a water-soluble anion. The molar percentage of ethanolamine to Jeffamine(copyright) XTJ-506 can range from about 50:50 to about 99:1, preferably from about 90:10 to about 75:25.
Exemplary water-soluble anions encompassed by R4 include, but are not limited to, chloride, carboxylate, sulfate, phosphate, nitrate, fluozirconate, fluotitanate, fluosilicate, mixtures of any of the foregoing and the like. Preferably R4 is a phosphate anion. As would be understood by one skilled in the art in view of the present disclosure, neutralization of the compound of Formula 2 with exemplary acids such as hydrochloric, oxalic, acetic, sulfuric, phosphoric, phosphorous, nitric, hexafluozirconic, hexafluotitanic, hexafluosilicic, and the like yields the compound of Formula 3.
The compounds of the present invention can be prepared via a multi-step process involving the generation of an intermediate or single step process. As an example of a multi-step synthesis a secondary amine is reacted with a molar equivalent of aldehyde and phenolic compound in a 1:1:1 molar ratio under conditions known to those skilled in the art to yield predominantly a mono-substituted phenolic Mannich adduct. The Mannich adduct is then further reacted with a primary amine and aldehyde in a 1:1:2 molar ratio, respectively, to yield a polyphenolamine composition. During this second step rearrangement reactions are possible that result in the formation of polyphenolamine species higher in molecular weight than would be anticipated based solely on the reactant stoichiometry. In a single step process there is no secondary addition of an amine, aldehyde, or phenolic reactant.
The compounds of the present invention can be utilized as produced or purified by methods known to those skilled in the art. For example, the products can be subjected to distillation, precipitation, liquid extraction, solid extraction (e.g., activated carbon), or like techniques to minimize the presence of undesirable residual reactants.
It is also an aspect of this invention that the polyphenolamine compounds can be prepared in such a manner that the resulting residual phenol and aldehyde levels are extremely low. For example, conducting the Mannich reaction first under basic conditions at 75-100xc2x0 C. under atmospheric conditions, pH adjusting acidic, further reacting at 75-100xc2x0 C. under atmospheric conditions, and optionally concentrating, yields a concentrated product (25-100 wt. % as the free base amine) in which the residual phenolic and formaldehyde reagents are in the parts per million (ppm) range as product.
The composition of the present invention is particularly effective as a post-treatment for a metal substrate. The term xe2x80x9cpost-treatmentxe2x80x9d refers to the treatment of a metal substrate which has undergone conversion coating. Treatment of a metal substrate having a bare metal surface is also within the scope of the present invention. Typical metal substrates include, but are not limited to zinc and its alloys, aluminum and its alloys, iron, tin, copper and its alloys, and cold-rolled, ground, pickled, hot-rolled and galvanized steel. When employed as a metal surface post treatment, the composition of the present invention is preferably supplied as an aqueous solution. The composition of the present invention may be water-soluble or water dispersible. To provide the desired water solubility or water dispersability, an organic acid or inorganic acid can be used for protonization or quatemization. Organic or inorganic acids may be employed to provide acidic character (pH) to the composition and assist in solublizing or dispersing the treatment composition. Many such acids are known in the art. Preferably, acids employed are acids of strongly coordinating anions such as fluoroacids including hexafluorozirconic, hexafluorotitanic and hexafluorosilicic acids, phosphoric acid, sulfuric acid, hydrochloric acid, oxalic acid and acetic acid. Mixtures of compatible acids may also be employed to provide the desired pH to the aqueous composition. Bases, such as NaOH, KOH, and NH4OH may be employed to provide basic character to the composition and assist in solubilizing the treatment compound should such be necessary. Other bases which may be suitable will be apparent to those skilled in the art in view of the present disclosure. Mixtures of compatible bases may also be employed.
The pH of the aqueous metal post treatment solution can vary from about 2.0 to 10.5. The preferred pH is from about 4.5 to 5.5 for the aqueous metal treatment solution. The aqueous metal treatment solution of the present invention will be used in a working bath at a dilute concentration from that of the composition as produced by the Mannich reaction or that of the composition during storage and/or transportation. A concentrate solution of the composition may comprise up to about 25% by weight based on active ingredients of the treatment composition. From a commercial point of view, a suitable concentrate of the present invention may comprise from about 1 weight % to about 10 weight % of the treatment composition.
Optional materials, which may be included in the post treatment solution of the composition of the present invention, include those materials commonly employed in corrosion inhibiting and adhesion promoting compositions. Exemplary of such materials are dispersing agents, foam control agents, pigments, adhesion promoters and solubilizers such as polyacrylic acid, polyamines, and polyphenols and compatible corrosion inhibitors. As in a typical metal treatment operation, the metal to be treated with the aqueous composition of the present invention is preferably initially cleaned by a chemical or a physical process and water rinsed to remove grease and dirt from the surface. The metal surface is then conversion coated, rinsed and brought into contact with the post treatment solution of the present invention. The present invention is useful to coat a broad range of metal surfaces, including zinc and its alloys, aluminum and its alloys, iron, tin, copper and its alloys, and cold-rolled, ground, pickled, hot-rolled and galvanized steel surfaces. The metal surface may be in any physical form, such as sheets, tubes or rolls.
The corrosion inhibiting adhesion promoting composition of the present invention may be applied to metal surfaces in any convenient manner. Thus, it may be sprayed, painted, dipped, or otherwise applied to the metal surface. The temperature of the applied solution can vary over a wide range, from the solidification temperature of the solution or dispersion to the boiling point of the solution or dispersion. During application to the metal surface, the temperature of the composition of the present invention is preferably between 20xc2x0 C. and 80xc2x0 C., more preferably between about 20xc2x0 C. and 55xc2x0 C. It is generally believed that a substantially uniform layer of the corrosion inhibitor/adhesion promoter coating should be deposited on a metal surface. It is also believed that something approaching a molecular layer is sufficient to achieve the desired results. Useful contact time can range from about 0.25 to about 5 minutes with contact times between 0.25 and 1 minute being sufficient at about room temperature. As will be apparent to those skilled in the art in view of the present disclosure, the treatment time and temperature of the applied composition may vary from those described. Selection of optimal composition and method parameters, such as concentrations of the polyphenolamine composition in the treatment bath, pH, optional materials, contact time, and bath temperature during coating would be dependent, in part, on the particular substrate, processing conditions and final coating desire. As such, selection of such parameters will be within the skill of those in the art, in view of the present disclosure.
After application of the treatment solution to the metal surface, the surface is preferably rinsed. Such rinsing is optional for a non-phosphated metal surface, although, in either case, good results can be obtained without rinsing after application of the treatment. Next, the treated metal surface is dried. Drying can be carried out by, for example, circulating air or oven drying. While room temperature drying can be employed, it is preferable to use elevated temperatures to decrease the amount of drying time required. After drying, the treated metal surface is ready for painting or the like. The surface is suitable for standard paint or other coating application techniques such as brush painting, spray painting, electrostatic coating, dipping, roll coating as well as electro-coating as a result of the treatment of the present invention. Application of the treatment compound of the present invention to a metal surface improves paint adhesion and corrosion resistance characteristics.
The present invention will now be further described with reference to a number of specific Examples which are to be regarded as illustrative and not as restricting the scope of the present invention.